1. Field of the Invention
The present invention relates to image forming apparatuses such as a copier and a printer. In particular, the invention relates to a subunit attaching structure and a subunit attaching/removing method that improve the workability of subunit replacement work in an image forming apparatus of a type in which a subunit for image formation is attached to a main body frame in a detachable manner.
2. Description of the Related Art
In conventional color image forming apparatuses, it is a common procedure that toner images of the respective color components are formed according to such an imaging method as electrophotography and then transferred to a recording member directly or via an intermediate transfer member so as to be superimposed one on another.
For example, tandem image forming apparatuses are known in which plural image carrying units (e.g., photoreceptor units in a case where electrophotography is employed) for formation of images of the respective color components that are yellow, magenta, cyan, and black, for example, are provided parallel and a belt unit as a transfer unit in which, for example, a transport belt that is wound on plural tension rollers circulates is opposed to the image carrying units. Toner images of the plural colors that are formed in the respective image carrying units are sequentially transferred to the transport belt of the belt unit or a recording member (a sheet of paper or an OHP sheet) that is placed on the transport belt so as to be superimposed one on another (e.g., Japanese Unexamined Patent Publication No. Hei. 6-110290).
In color image forming apparatuses of the above kind in which toner images of the respective color components are sequentially transferred to a recording member or an intermediate transfer member so as to be superimposed one on another, registration among the toner images of the respective color components is an important factor.
In particular, in tandem image forming apparatuses in which image carrying units are provided for the respective color components, they are associated with a technical problem that a registration error is prone to occur if a deviation occurs in the alignment between the main body frame and each image carrying unit or the belt unit.
To effectively prevent such a registration error, the present assignee proposed a technique that misalignment of each subunit is prevented by forming positioning portions for image carrying units and a belt unit integrally with a main body frame (Japanese Patent Application No. Hei. 11-241625), a technique that image carrying drums such as photoreceptor drums or a transport belt is prohibited from axial movement in a state that image carrying units or a belt unit is positioned and fixed (e.g., Japanese Unexamined Patent Publications Nos. 2000-310921 and 2000-128382), and other techniques.
Incidentally, in many image forming apparatuses of the above kind, image carrying units such as photoreceptor units are CRUs (customer replaceable units) that can be replaced by a user. In this case, naturally, work of replacing the image carrying units needs to be performed frequently.
In such a case, if work of replacing each image carrying unit can be performed independently of units around it, such work would be relatively easy.
However, due to a layout-related restriction such as a restriction that each image carrying unit needs to be located under the belt unit, there may occur, for example, a case that the belt unit needs to be located at such a position as to obstruct work of replacing the image carrying units.
In an image forming apparatus of the above type, before doing work of replacing the image carrying units, the belt unit that will obstruct such work needs to be moved away from the image carrying units.
Therefore, every time the image carrying units are to be replaced, it is necessary to remove the belt unit from the main body frame and then re-attach the belt unit to the main body frame after completion of replacement of the image carrying units. However, in image carrying unit replacement work, an operation of removing the belt unit each time and placing it outside the main body of the image forming apparatus and an operation of re-setting the belt unit that is placed outside the main body of the image forming apparatus after mounting of new image carrying units are very cumbersome.
When the image carrying units are replaced or the belt unit is removed to replace the image carrying units, it is necessary to again position and fix new image carrying units or the belt unit at its regular position in the main body frame. For example, in positioning an image carrying unit (or the belt unit) with respect to the main body frame and fixing the former to the latter, if the image carrying unit (or belt unit) is positioned with respect to the main body frame and fixed to the latter before the image carrying unit (or belt unit) is prohibited from axial movement, friction between the image carrying unit (or belt unit) and positioning portions of the main body frame makes it difficult to move smoothly the image carrying unit (or belt unit) to its axial movement prohibiting position, which is a factor of causing a registration error.
The present invention has been made in view of the above circumstances in the art, and provides a subunit attaching structure and a subunit attaching/removing method in an image forming apparatus that can improve the workability of subunit replacement work and position and fix a subunit at a regular position easily and correctly.
According to a first aspect of the invention, there is provided a subunit attaching structure of an image forming apparatus in which plural subunits for image formation are attached to a main body frame in a detachable manner with a positional relationship that at least one of the subunits is located at such a position as to obstruct an operation of replacing another, comprising positioning portions that are provided on the main body frame and position the respective subunits; and a subunit releasing mechanism that is used in releasing at least part of the subunits from a state that they are positioned with respect to and fixed to the associated positioning portion, and that moves at least an outside subunit that obstructs an operation of replacing an inside subunit from a positioning and fixing position to a prescribed releasing position.
According to a second aspect of the invention, there is provided a subunit removing method of an image forming apparatus in which plural subunits for image formation are attached to a main body frame in a detachable manner with a positional relationship that at least one of the subunits is located at such a position as to obstruct an operation of replacing another, comprising, to remove at least part of the subunits, an outside subunit releasing step of canceling at least a state that an outside subunit that obstructs an operation of replacing an inside subunit is fixed to an associated positioning portion and releasing the outside subunit from the positioning portion; and an inside subunit releasing step of canceling a state that the inside subunit is fixed to an associated positioning portion and releasing the inside subunit from the positioning portion at the same as or after at least the outside subunit releasing step is executed.
According to a third aspect of the invention, there is provided a subunit attaching structure of an image forming apparatus in which plural subunits for image formation are attached to a main body frame in a detachable manner with a positional relationship that at least one of the subunits is located at such a position as to obstruct an operation of replacing another, comprising positioning portions that are provided on the main body frame and position the respective subunits; and a subunit fixing mechanism that is used in positioning at least part of the subunits being in a released state with respect to the associated positioning portions and fixing the former to the latter, and that holds at least an outside subunit that obstructs an operation of replacing an inside subunit at a prescribed releasing position and moves the outside subunit from the prescribed releasing position to a prescribed, positioning and fixing position.
According to a fourth aspect of the invention, there is provided a subunit attaching method of an image forming apparatus in which plural subunits for image formation are attached to a main body frame in a detachable manner with a positional relationship that at least one of the subunits is located at such a position as to obstruct an operation of replacing another, to attach at least part of the subunits, comprising, to attach at least part of the subunits, an inside subunit fixing step of positioning at least an inside subunit with respect to an associated positioning portion and fixing the former to the latter; and an outside subunit fixing step of positioning, with respect to an associated positioning portion, an outside subunit to be located outside the inside subunit and fixing the former to the latter, the outside subunit fixing step being executed after at least the positioning of the inside subunit fixing step is performed.
According to a fifth aspect of the invention, there is provided a subunit attaching structure of an image forming apparatus in which plural subunits for image formation are attached to a main body frame in a detachable manner with a positional relationship that at least one of the subunits is located at such a position as to obstruct an operation of replacing another, comprising positioning portions that are provided on the main body frame and position the respective subunits; a subunit releasing mechanism that is used in releasing at least part of the subunits from a state that they are positioned with respect to and fixed to the associated positioning portion, and that moves at least an outside subunit that obstructs an operation of replacing an inside subunit from a prescribed, positioning and fixing position to a prescribed releasing position; and a subunit fixing mechanism that is used in positioning at least part of the subunits being in a released state with respect to the associated positioning portions and fixing the former to the latter, and that holds at least the outside subunit that obstructs an operation of replacing the inside subunit at the prescribed releasing position and moves the outside subunit from the prescribed releasing position to the prescribed, positioning and fixing position, wherein the subunit releasing mechanism and the subunit fixing mechanism are a single mechanism.
According to a sixth aspect of the invention, there is provided a subunit attaching structure of an image forming apparatus in which a subunit for image formation is attached to a main frame body in a detachable manner, comprising a positioning portion that is provided on the main body frame and positions the subunit, the positioning portion comprising an axial movement prohibiting portion that prohibits in advance axial movement of the subunit before the subunit is positioned.
According to a seventh aspect of the invention, there is provided a subunit attaching structure of an image forming apparatus in which a subunit for image formation is attached to a main frame body in a detachable manner, comprising a two-direction positioning portion that prohibits movement of the subunit in a height direction and a horizontal direction on the main body frame; and a one-direction positioning portion that prohibits movement of the subunit only in the height direction, wherein the subunit is positioned preferentially with respect to the two-direction positioning portion over the one-direction positioning portion.